Preparation of fluoroform



3,042,727 PREFARATIGN Gi FLUQRQFURM Franciszek Olstowski, Freeport, andJohn Donald Watson, Lake Jackson, Ten, assignors to The Dow ChemicalCompany, Midland, Mich, a corporation of Delaware No Drawing. Filed June4, 1959, Ser. No. 817,984

7 Claims. (Cl. 260653) The present invention relates to a novel methodof preparing fluoroform. More particularly, the invention involves thevapor phase hydrogenation of trifluorornethylhalides.

An early method of preparing fluoroform involved the hydrogenolysis ofperfiuorocarbons. This process involved polycarbon starting compounds,and, by way of illustration, demonstrated that the singlecarbon-containing fluorocarbon would not accomplish the desired result,Simmons, U.S. Patent 2,494,064. Simmons, in US. Patent 2,519,983, laterdisclosed an electrochemical'process involving electrolyzing a liquid HFsolution containing a fluorinatable organic starting compound. However,this process was complicated by many by-products and involved corrosiveand physiologically dangerous materials.

More recently, Benning et al., in US. Patent 2,615,926, disclosed aprocess involving a non-catalytic hydrogenolysis of chlorine-containingfluorocarbons which required, as essential, at least 2 chlorine atoms.

The present invention is based on the discovery that hydrogen will reactreadily with compounds having the formula CF X, wherein X represents thehalogens Cl, Br and I, or mixtures thereof, at a temperature suflicientto liberate HX and produce fluoroform. Separation of fluoroform is thenreadily accomplished by conventional methods. While hydrogen gas ispreferred, other materials which generate hydrogen under the conditionsof reaction may be employed. Vapor phase trifluoromethylhalide is passedthrough the reaction tube together with hydrogen gas in a reactant moleratio of 1:4 to 4:1. Materially smaller proportions of hydrogen resultin a decrease in conversions and yields. A relatively high proportiongives the best conversions and yields, probably due to less degradationto HF.

Residence times, as used herein, are based on the time the reactantgases spend in that portion of the reaction tube that is within therange of 100 C. of the temperature indicated for the operation. In ourprocess, the residence times will be within the range of from about 0.1to seconds. Preferably, we employ a residence time of 0.5 to 1 second toobtain the best conversions and yields.

The reaction tube will be heated to temperatures of from about 450 C. toabout 900 C. At temperatures materially below 600 C., the conversion andyields are comparatively low. Temperatures materially above 900 C.generally cause excessive decomposition with the formation of carbon,hydrogen fluoride, hydrogen chloride and carbon tetrafluoride. Optimumconversion and yields are generally obtained at a temperature range of450 C. to 900 C.

The process will usually and preferably be carried out at asubstantially atmospheric pressure, that is, at a pressure of 1atmosphere. However, higher or lower variations in pressure have littleor no efiect on the results.

The presence of a copper catalyst is sometimes desirable but is notessential to the reaction. At lower temperatures the presence of copperresults in higher yields, while at higher temperatures, the presence ofcopper produces greater degradation to HF. Suitable copper catalystsinclude, for example, copper turnings, copper wire, copper shot, and thelike. Separation of the desired fluoroform is readily accomplished bycollecting and condensing the efiiuent gas and thereafter fractionallydistilling the resulting condensate.

The following examples are given to more clearly illustrate ourinvention but are not to be construed as limiting the invention thereto:

EXAMPLE 1 The reactor tube consisted of a 35 millimeter Vycor tubepacked with a 6-inch length of copper turnings and set in a 2 kilowattSentry tube furnace. Gaseous CF Cl and H were passed through the tube ina 1:1 mol ratio of H and CF C1 at a total gas flow rate of 1 cubic footper hour. The hot zone length of the Vycor tube.reactor was assumed tobeapproximately 6 inches long. Residence time of the reactants at theoperating temperatures ranged from 1.5 to 3 seconds.

An infra-red analysis of the exit gases showed the followingcompositions (in percent) produced at reaction temperatures of 500 C.and 700 C.:

T811111, C. OFaOI OFsH The remainder of the gases consisted of unreactedH and HCl. Some attack of the Vycor tube by HF was noted.

EXAMPLE 2 Using a 15 millimeter Vycor tube heated by a 2 kilowatt Sentryfurnace without copper turnings, an approximately 1:1 mol ratio of H andCF Cl was fed through the reactor at a total gas rate of 1 cubic footper hour.

The product gases showed the following compositions (in percent)produced at various reaction temperatures:

Temp., 0. OFsOI CFaH The remainder of the gases were assumed to behydrogen.

EXAMPLE 3 Temp., C. OFsBr OF H 4m 68 Trace 450 67 2. 3 500 67 11. 6 55048 52 600 32 46 70 were conducted and the data thus obtained aresummarized in Table I.

Patented July 3, 1962 tends to give the best yields Table I V Flow Rate,Reaeted F to,

Ex. Temp., ttfi/hr. Residence GF O1, OFaCl, CFQH, HF, percent Yield No.-0. 'lgime, Grams percent percent Grams CF51 Table 1 shows that at 750"0.. a high H to CF Cl ratio of CF H. The conversion penpass is muchbetter. at 825 C. than at 750 C. but the yield is not so sensitive to Hto CF Cl feed ratio at the higher temperature. The analysis ofCF Cl andCF H was an infra-red: acid free analysis, and the CF H yield data wasbased on. fluorine content.

r In a manner similar to that of the foregoing examples;trifluoromethliodide may be substituted for the triiiuoromethylchlorideor trifluoromethylbromide specifically shownwith substantially the sameresults. 7

Various modifications may be made in the present invention Withoutdeparting from the spirit or scope thereof audit is to be understoodthat welimit ourselves only as defined in the appended claims.

1. A process of preparing fluoroform Whichcomprises contacting hydrogenanda compound having-the formula CF X, wherein X represents a halogenselected from the group: consisting of Br and I, at a temperatureranging from about 450 C. to about 900? C. for a residence time rangingfrom about 0.1 second to about 10 seconds, and separating fluoroformfrom thereactionproduct.

' 2. A process of preparing fluoroform which comprises 7 contactinghydrogen and a compound having the formula CE X vvherein X represents ahalogen selected from the group consisting of C1,.Br and I, at atemperature ranging from 450 C. to about 900 .C. fora residence timeranging from about 0.1 second to about 10 seconds, in the presence of acopper catalyst, and separating fiuoroform from the reaction product. 3.A process of preparing fiuoroform which comprises contacting hydrogenanda mixture of the compounds 7 having the formulaCF X;,vvherein Xre'presents arhalogen selected from the group consisting of Cl, Br andI, at a temperature ranging from about 450 C. to about 900 C. .7

for a residence time ranging from about. 0.1 second to about 10 secondsand inthe presence of a copper catalyst, and separating fluoroformfrom-the reaction product.

4. A process of preparing fluoroform which comprises contacting hydrogenand .nifluoromethylchloride at a temperature ranging from about 600C. toabout 900.

C. for a residence time ranging from about 0.1 second to about ,10seconds, and separating fluoroformfrom the reaction product.

5. A process of preparing fluoroforrn which comprises contactinghydrogen and trifluorornethylchloride at a temperatureranging from about600 C. to about 900 C. for a residence timeranging from about 0.1 secondto about 10 seconds and intne presence of'a copper catalyst, and.separating fluoroform from the reaction product. 6. A process ofpreparing fluoroform which comprises contacting hydrogen and'trifluoromethylbromide at a temperature ranging'jfrom 450 Cpto about900 C. for.

a residence time ranging from about 0.1 second to about 10 seconds, andseparating fluoroform from the reaction product.

' 7.. A process of preparingifiuoroform which comprisescontactinghydrogen and trifluoromethyl bromide at a temperature ranging from 450C. to about 700 C. for a residence time ranging from about 0.1 second toabout 10 seconds; and separating fluoroform from the reaction product. 7g s Y References Cited in the file of this patent l UNITED STATESPATENTS g, 6 15, 92s Bordner Oct-28, 1952 V OTHER' REFERENCES 7Haszeldine: Journal oftheChemical Society (London) (1952 pagei25l0relied o

1. A PROCESS OF PREPARING FLUROFORM WHICH COMPRISES CONTACTING HYDROGENAND A COMPOUND HAVING THE FORMULA CF3X, WHEREIN X REPRESENTS A HOLGENSELECTED FROM THE GROUP CONSISTING OF BR AND 1, AT A TEMPERATURE RANGINGFROM ABOUT 45/*C. TO ABOUT 900*C. FOR A RESIDENCE TIME RANGING FROMABOUT 0.1 SECOND TO ABOUT 10 SECONDS, AND SEPARATING FLUOROFORM FROM THEREACTION PRODUCT.
 2. A PROCESS OF PREPARING FLUROFORM WHICH COMPRISESCONTACTING HYDROGEN AND A COMPOUND HAVING THE FORMULA CF3X, WHEREIN XREPRESENTS A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CI, BR AND I,AT A TEMPERATURE RANGING FROM 450*C. TO ABOUT 900*C. FOR A RESIDENCETIME RANGING FROM ABOUT 0.1 SECOND TO ABOUT 10 SECONDS, IN THE PRESENCEOF A COPPER CATALYST, AND SEPARATING FLUOROFORM FROM THE REACTIONPRODUCT.